1. Field of the Invention
The present invention relates to computer programming, and deals more particularly with extending a model in a manner that is transparent to the model being extended.
2. Description of the Related Art
Object-oriented models can be expressed generally as a group of class diagrams, collaboration diagrams, state diagrams, etc. A modeling notation such as the well-known Unified Modeling Language (“UML”) may be used to describe the model. Once a model is created, it is possible to represent it in a programming language such as the Java™ programming language. (“Java” is a trademark of Sun Microsystems, Inc.) The instance of the model then becomes available as a programming tool.
Some models provide an extension framework. This means that the user can augment the model with one or more new objects (or a new model entirely) not defined in the original specification, as long as they conform to certain constraints set forth by the model. An example of this is the Web Services Description Language (“WSDL”) model. WSDL is a well-known language for describing network-accessible services. The WSDL model provides an extension framework where an “ExtensibleElement” (i.e., an element defined in the WSDL, or extended, model) can be extended by an “ExtensibilityElement” (where this element is implemented by the extending model). This constraint is somewhat limiting because the objects in the extending model need to implement the “ExtensibilityElement” interface, and therefore create a dependency on the extended model. This dependency prevents a model extension from being reusable when extending other models. Also, the extension framework must be explicitly provided by the model in order for other models to “plug in” to it.